Intercalibration of GOES 8-15 solar proton detectors

This work provides a relative intercalibration of the high-energy proton channels from the Energetic Particle Sensors (EPS) flown on the Geostationary Operational Environmental Satellites (GOES) since 1994 using a technique that depends on features that arise during high solar wind dynamic pressure. Based on observations of solar energetic protons from polar-orbiting and geostationary satellites (1998-2013), solar proton fluxes are isotropic at geostationary orbit during periods of high solar wind dynamic pressure (P-dyn>5-10nPa). The observed isotropy results from the solar proton fluxes having rigidities (momenta per unit charge) greater than their geomagnetic cutoffs over the complete energy and angular responses of the satellite-borne detector. (The cutoff in a given direction is the rigidity below which an interplanetary particle cannot reach that location.) Under these conditions, we determine the relative responses of the EPS flown on GOES 8 through 15. These detectors are widely used for alerts of the radiation hazard posed to spacecraft and humans by solar energetic particle events; therefore, it is important to know their relative responses. The results of this low-scatter intercalibration analysis show that the relative responses agree to 20% or better (sometimes better than 1%). The effect of such relative calibration differences on the derived integral fluxes used by NOAA for its real-time solar radiation storm alerts is shown to be small (<10%). This method can be used to intercalibrate solar proton detectors of different design if their broad energy response functions are carefully accounted for.